Sizing compositions are used to improve processing properties of glass or carbon fibers, such as: fiber bundle cohesion, bundling, spreadability, fluff formation resistance, fiber smoothness and softness, abrasion resistance and easy and nondestructive unwindability of bobbined fiber bundles. Sizing also affects the physical properties of the composite containing the treated fibers.
The reinforced plastic industry has been using glass fibers in various forms for reinforcing polymeric matrices to produce a variety of products. Glass fibers have been used in the form of continuous and chopped filaments and strands and rovings and woven and nonwoven fabrics to reinforce polymers. Thermosetting polymeric matrices have been reinforced with a variety of different forms of glass fibers resulting in the production of products such as: sheet molding compounds, bulk molding compounds, pultrusion products, panel products, spray up molding products, etc.
Production of glass fibers for the polymeric reinforcement market involves, attenuation of the glass fibers from molten streams of fiberizable glass material from a bushing or like device connected to a furnace containing molten fiberizable glass material. The glass fibers are attenuated by conventional means such as winders or pull wheels. In the process of producing glass fibers, a chemical composition is applied to them shortly after they are attenuated as the molten streams of glass. Prior to the present invention, the chemical composition has traditionally been an aqueous solution, foam or gel composition containing film forming polymeric materials, coupling or keying agents, lubricants and sometimes processing aids. This chemical composition or sizing is necessary in order to retard inter filament abrasion of the glass fibers when they are gathered into a bundle of glass fibers or strands. It is also required in order to make the glass fibers compatible with polymer matrices that they are used to reinforce. After application of the sizing, the fibers are then dried either in the package form or in the chopped strand form before they are used for reinforcement.
A number of reinforcement applications require the use of large bushings with tip plates having as many as 4000 tips. Such tip plates or bushings operate for days at high temperatures of from about 1500 to about 1620 degrees C (2850 F to 2950 F). Conventional high temperature bushing plates operate at elevated temperatures of about 2200.degree. F. This creates a number of problems.
In particular, the high temperatures created by the large bushings as well as the unrestricted air flow into the heat transfer chambers results in inefficient and nonuniform cooling across the fiber fan between the bushing and the size applicator roller. This further results in changes to the wetting characteristics of the size being dispensed to the applicator. It also appears to negatively affect the surface tension of the sizing particularly at the center of the applicator. This results in the sizing being applied and dispersed nonuniformly across the width of the fan. Specifically, the fibers at the exterior edges of the fan are typically cooler than those at the middle of the fan. As a result, greater amounts of the sizing composition are applied to the fibers on the outer edges of the fan than is applied to the fibers in the interior region of the fan. Further, the fibers located in the interior portion of the fan can remain so hot that they do not receive or retain sufficient amounts of the size composition.
A number of attempts have been made to compensate for the problem of nonuniformity of size on the applicator. For example, there has been considerable work in the area of devising a means to control the flow of air through the chamber so as to achieve uniform and adequate cooling of the fibers across the width of the fiber fan such that they pick up sufficient and substantially uniform quantities of sizing material from the size applicator roller. This means of addressing the problem may be found in copending U.S. patent application filed concurrently herewith, the disclosure of which is hereby incorporated herein by reference. However, there exists a need for a sizing that improves the uniformity of size film on the applicator rolls.
The present invention provides a sizing that allows for a method of controlling the uniformity of the size film on the applicator roll. In addition, the invention results in a size that has a wider temperature stability.